A film formation method based on sputtering phenomenon in which ion (for example Ar ion) is caused to collide with a target material in a vacuum to cause atoms of the target to pop up from the target material and deposit on a substrate disposed opposite to the target material, is conventionally well-known.
According to a magnetron sputtering film formation method, which is one of methods based on the above sputtering phenomenon, a tunnel-shaped magnetic field is formed over a target surface to capture secondary electrons generated during a process of the sputtering phenomenon by Lorentz force and cause the secondary electrons to conduct their cycloid motion, thereby increasing a frequency of ionization collision of the secondary electrons with Ar gas. Thereby, high-density plasma is produced in a space lying in the vicinity of the target surface, thereby making a film formation rate higher.
Such a magnetron sputtering film formation method, however, has a drawback that, because a target material in a stronger magnetic field is locally eroded faster by the sputtering, a sputtering amount in a plane of the target material becomes non-uniform, decreasing target utilization efficiency. For this reason, various techniques have thus far been developed to overcome this drawback.
For example, a quadridirectional magnetic field producing technique has been proposed in which three magnets each having a N-S magnetic direction (i.e., magnetic moment) parallel with the target surface and two magnets each having a N-S magnetic direction perpendicular to the target surface are suitably combined together to produce in a target region a tunnel-shaped, closed-loop quadridirectional magnetic flux comprising upper, lower, inner and outer magnetic fluxes (hereinafter referred to as “quadridirectional magnetic field”), and thereby magnetic flux densities of these magnetic fluxes cancel each other so that a zero point at which a net magnetic flux density becomes zero can be positioned in the target region (see patent document 1).
According to such a magnetic field producing technique, uniformity of plasma in the target region (i.e., sputtering region) during erosion and removal of the target material by plasma discharge (i.e., glow discharge) is increased, improving the target utilization efficiency.    Patent document 1: Japanese Patent No. 3473954 specification (FIG. 3)